OT30051 | Capital Gains: Undeveloped Areas - Definition of Oil
From HM Revenue & Customs · Oil Taxation Manual
Oil in relation to a UK licence has its PRT meaning and generally includes any hydrocarbons won under a UK or UK Continental Shelf oil licence.
In relation to other licences it means any petroleum within the meaning of the Petroleum Act 1998 (TCGA92\S196(5)).