Texas Supreme Court Limits Working Interest Profit Sharing to Oil Only, Rejecting Extrinsic Evidence of Course of Dealing

The Texas Supreme Court reversed summary judgment for lessors who claimed entitlement to working interest gas proceeds under a 1932 oil and gas lease, holding that the unambiguous lease language reserved to lessors only one-half of working interest oil profits, not gas. Despite Sun Oil's decades-long practice of voluntarily paying lessors a share of working interest gas proceeds, the Court rejected the use of extrinsic evidence and estoppel theories to create contractual obligations not expressed in the integrated writing.