Background and Procedural Posture

Lessors sued Sun Oil Company (Delaware) for declaratory judgment and damages, claiming entitlement under their oil and gas lease to one-half of the working interest gas proceeds. The District Court of Montgomery County granted summary judgment in favor of the lessors, and the Beaumont Court of Civil Appeals affirmed. Sun Oil appealed to the Texas Supreme Court, which reversed.

The Central Dispute

The parties agreed that the lease was unambiguous but disagreed fundamentally on its meaning. Lessors argued the lease entitled them to one-half of all working interest production—both oil and gas. Sun Oil contended the lease obligated it to account to lessors only for working interest oil, not gas. For years, Sun Oil had paid lessors a share of working interest gas proceeds, but later ceased these payments and revoked the division orders, asserting no such obligation existed under the lease terms.

The Court's Analysis of Contract Language

Chief Justice Greenhill, writing for the Court, emphasized the foundational principle of contract interpretation:

An unambiguous instrument will be enforced as written; in the ordinary case, the writing alone will be deemed to express the intention of the parties.

The Court held that construction of the unambiguous oil and gas lease demonstrated that the lease did not obligate Sun Oil to account to lessors for any part of working interest gas. The Court found that the lease's profit-sharing provision applied only to oil, and therefore resort to extrinsic evidence to create an obligation regarding gas was improper.

Rejection of Extrinsic Evidence

The Court rejected lessors' attempt to rely on surrounding circumstances or Sun Oil's course of dealing to alter the plain meaning of the lease. Applying established principles of contract interpretation, the Court held that when interpreting an integrated writing, the parol evidence rule circumscribes the use of extrinsic evidence. The Court explained that evidence of surrounding circumstances may be consulted in construction of a contract, but only as an aid in understanding the contract's language. Where the language appears capable of only a single meaning, the court must confine itself to the writing. The Court stated:

Only where a contract is first found to be ambiguous may the courts consider the parties' interpretation; where the meaning of the contract is plain and unambiguous, a party's construction is immaterial.

Estoppel Claims Rejected

The Court also rejected lessors' estoppel argument based on Sun Oil's voluntary payments over the years. The Court held that estoppel is a defensive theory and does not create a contract right that does not otherwise exist. Since the lease did not obligate Sun Oil to account to lessors for any part of working interest gas, Sun Oil's conduct in paying lessors a share of the working interest gas did not create a right in lessors to continue receiving such payments in perpetuity. The Court further noted that damages recoverable by a party claiming estoppel are not measured by the profits that such party's reliance led them to expect, but instead are limited to the amount necessary to compensate that party for a loss already suffered.

Holding

The Texas Supreme Court reversed the lower courts' judgments, holding that the unambiguous lease language did not obligate Sun Oil to pay lessors any share of working interest gas proceeds. The Court's decision reinforced the principle that courts will not use extrinsic evidence or equitable doctrines to rewrite clear contractual terms, even when one party has voluntarily performed beyond its obligations for an extended period.