This article, repealed by Royal Decree M/70 with effect from 1 January 2018, previously governed the tax base for natural gas investments. It stipulated that the tax base for each gas exploration and production contract was to be treated as independent from any other contract. Consequently, taxpayers were required to file separate tax declarations and audited closing accounts for each individual agreement. Furthermore, the natural gas investment tax base was mandated to be completely separate from the tax base of any other unrelated business activities, which also necessitated separate tax filings and accounts.