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A tax stabilization agreement is a host state’s contractual promise to a foreign investor. Under it, the tax rules in force at signing stay fixed for an agreed term, or the state offsets any change. Broader stabilization clauses cover the whole legal regime. Mining, energy and concession investors use them to lock in the deal. Generally, tribunals enforce them through compensation.
What a Stabilization Clause Does
Sooner or later, governments change tax rates, royalties, export rules and permits. For a 20-year mining or power project, that risk is real. Therefore, investors ask the host state to commit, in the contract itself, that the rules will stay fixed. In practice, the stabilization clause appears in concession agreements, production-sharing contracts, mining conventions and public-private partnership contracts.
Of course, the clause does not stop a legislature from acting. Instead, it changes the consequences. If the state breaks its promise, the investor can claim damages under the contract. Moreover, the promise often supports a treaty claim for breach of fair and equitable treatment. After all, it creates a specific assurance that the investor relied on.
A stabilization clause works best alongside other protections. These include an international arbitration clause, a governing-law clause, a waiver of sovereign immunity and coverage under a bilateral investment treaty. Likewise, an umbrella clause in the treaty can elevate the contractual promise into a treaty obligation.
Three Types of Stabilization Clause
A 2008 study prepared for the International Finance Corporation and the UN Special Representative on business and human rights sorted stabilization clauses into three groups.
- Freezing clauses. These freeze the law of the host state for the project over its life, so new laws simply do not apply to the investment.
- Economic equilibrium clauses. Here, the investor must comply with new laws. However, the state must compensate it for the cost of compliance, for example through tariff adjustments, tax relief, a longer concession term or money.
- Hybrid clauses. Finally, these require the state to restore the investor to its prior position, including through exemptions from new laws where the contract says so.
Notably, the study found full freezing clauses mainly in extractive projects outside the OECD. By contrast, contracts from OECD countries mostly used limited economic equilibrium clauses that cover only discriminatory changes in law. Consequently, the drafting choice says a lot about the bargaining power of each side. In that sample, 83 percent of full freezing clauses sat in mining projects.
How Arbitral Tribunals Treat Stabilization Clauses
Aminoil: a general clause does not block nationalization
In Kuwait v. American Independent Oil Co. (Aminoil), Award of 24 March 1982, 21 ILM 976, Kuwait ended a 1948 oil concession by Decree Law No. 124 of 1977. Article 17 of the concession barred the Ruler from annulling the agreement by legislation or administrative measures. It read: “The Shaikh shall not by general or special legislation or by administrative measures or by any other act whatever annul this Agreement.” Nevertheless, the tribunal held that a contractual bar on nationalization must be express and limited in time. A general clause in a 60-year concession could not freeze the state’s sovereign powers for that long. The takeover was therefore lawful, but Kuwait still owed compensation.
Parkerings: no stabilization clause, no frozen law
In Parkerings-Compagniet AS v. Lithuania, ICSID Case No. ARB/05/8, Award of 11 September 2007, the investor claimed that legal changes in Vilnius frustrated its expectations. However, the tribunal disagreed. A state may enact, change or repeal laws at its discretion. Unless the investor holds a stabilization clause or a specific assurance, a change in the regulatory framework is not unfair in itself. In other words, the clause is what converts a hope into a protected expectation.
Duke Energy v. Peru: a tax stabilization agreement enforced
In Duke Energy International Peru Investments No. 1 Ltd. v. Peru, ICSID Case No. ARB/03/28, Award of 18 August 2008, the dispute concerned a tax stabilization agreement, in the form of a Peruvian legal stability agreement signed in 2001. Subsequently, Peru’s tax authority assessed back taxes against the investor’s power company. The tribunal found that one of those assessments breached the agreement’s guarantee of tax stabilization. Significantly, it treated the agreement as a private-law contract enforceable against the state.
Tax Stabilization Agreement in Practice: Peru and Honduras
Some countries write stabilization into statute. Peru is a prominent example. Under Article 1357 of its Civil Code, the state may grant guarantees by contract. In addition, Article 62 of the Constitution provides that later laws cannot modify contract terms. Article 39 of Legislative Decree No. 757 then gives legal stability agreements the force of law, so the state cannot change or end them unilaterally. In Duke Energy, the tax stabilization agreement ran for ten years and froze the income tax regime, among other rights.
By contrast, Honduras offers a cautionary tale. Its 2013 ZEDE Law allowed the technical secretary of each zone to sign legal stability agreements with investors. The law also provided that, if repealed, it would remain in force for the term of those agreements. That term could not be shorter than ten years. On 9 March 2021, Honduras Próspera signed such an agreement. It provided for stabilization until 15 January 2064 or ten years after any repeal, although Honduras disputes that it binds the Republic. Then, in April 2022, Congress repealed the ZEDE Law with immediate effect.
Honduras Próspera and the 2026 ICSID Return
Subsequently, the investors filed ICSID Case No. ARB/23/2 in December 2022 under CAFTA-DR and the stability agreement. Honduras then denounced the ICSID Convention, and the denunciation took effect on 25 August 2024 under Article 71. However, Article 72 preserves consent given before the notice, so the case continued.
On 26 February 2025, the tribunal rejected Honduras’ preliminary objection that the investors had to exhaust local remedies first. Its decision on preliminary objections held that the no-U-turn waiver in CAFTA-DR Article 10.18.2 is incompatible with such a requirement. In any event, a constitutional challenge would have been futile, because the Supreme Court had already declared the entire ZEDE framework unconstitutional in 2024. The merits remain pending.
Meanwhile, the policy climate shifted. President Nasry Asfura signed the ICSID Convention on 6 March 2026. Honduras deposited its instrument of ratification on 17 July 2026, and the Convention re-entered into force for Honduras on 16 August 2026. For investors, the lesson is clear: a stability clause is only as strong as the forum that will enforce it.
Human Rights Limits on Stabilization
At the same time, stabilization clauses have drawn criticism for freezing labor, environmental and safety laws. The UN Guiding Principles on Business and Human Rights respond in Principle 9. States should keep adequate domestic policy space to meet their human rights obligations when they conclude investment treaties or contracts.
The UN Principles for Responsible Contracts go further. Principle 4 addresses stabilization clauses directly. If used, they should not interfere with the state’s bona fide, non-discriminatory efforts to meet its human rights obligations. In its words, such clauses “should be carefully drafted so that any protections for investors against future changes in law do not interfere with the State’s bona fide efforts to implement laws, regulations or policies, in a non-discriminatory manner, in order to meet its human rights obligations.” Accordingly, modern clauses increasingly carve out non-discriminatory laws on health, safety, labor and the environment. Investors who accept such carve-outs often gain a more durable bargain.
Drafting a Stability Clause: Practical Checklist
- Define the scope. State whether the tax stabilization agreement covers income tax and royalties only, or the whole legal regime. Also list the laws in force on the signing date.
- Choose the mechanism. A freezing clause offers certainty but invites political backlash. Alternatively, an economic equilibrium clause with a clear rebalancing formula is easier to defend.
- Set a realistic term. The Aminoil tribunal expected a bar on nationalization to be express and limited in time, so avoid open-ended promises.
- Add triggers and timelines. Specify what counts as a change in law and who may invoke the clause. Then set how long renegotiation lasts before arbitration.
- Carve out bona fide regulation. Exclude non-discriminatory health, safety, labor and environmental measures, in line with the UN principles.
- Secure the forum. Pair the clause with an ICSID or other international arbitration clause, a waiver of sovereign immunity and a governing-law clause. Consent under Article 25 of the ICSID Convention can be given in the contract itself.
- Check treaty coverage. Structure the investment so that a treaty with fair and equitable treatment protection applies as a second layer of defense.
- Plan enforcement. An ICSID award binds the parties under Article 53. Moreover, every member state must enforce its pecuniary obligations under Article 54. That article requires each member state to enforce the award’s pecuniary obligations “as if it were a final judgment of a court in that State.” In the United States, 22 U.S.C. § 1650a gives such awards the same effect as a final state-court judgment. Our guide to enforcing an ICSID award explains the steps.
Our investment disputes practice reviews these provisions at the negotiation stage and in disputes. Likewise, our pages on ICSID arbitration and indirect expropriation explain the treaty tools that complement a stabilization clause.
Frequently Asked Questions
Yes, generally, as a contract. Tribunals in Aminoil and Duke Energy v. Peru treated the stabilization promise as binding. However, the usual remedy is compensation, not an order that the old law be restored.
In short, a freezing clause excludes new laws from the project altogether. An economic equilibrium clause lets new laws apply but obliges the state to restore the investor’s financial position. Hybrid clauses combine both approaches.
Not automatically, as a rule. In Aminoil, the tribunal held that a bar on nationalization must be express and limited in time. Otherwise, the state may nationalize lawfully, provided it pays appropriate compensation.
Yes, provided that an investment treaty applies. Still, Parkerings v. Lithuania shows that general changes in law are rarely a treaty breach unless the state gave a specific assurance or acted unfairly.
Conclusion
In sum, a tax stabilization agreement, or a broader stabilization clause, is one of the few tools that addresses political risk inside the contract itself. It will not freeze a sovereign forever, as Aminoil shows. Yet it converts a change in law into a compensable breach, as Duke Energy v. Peru and the pending Próspera case illustrate. Careful drafting, a credible forum and treaty coverage turn the clause from a comfort letter into real protection.
Contact our team to discuss a tax stabilization agreement, treaty coverage and dispute options tailored to your project.
