Venezuela is laying claim to massive oil and gas reserves recently discovered by Exxon Mobil off the coast of Guyana, reported the Chicago Tribune.

The two South American countries have long been tied together as participants of a bilateral “oil for rice” deal, but relations have suffered since the announcement by Exxon of the reserves.

Guyana is a small, impoverished country with a population of less than 1m. Current estimates for the total value of the recently discovered deposits is around $40bn, a huge sum for the tiny nation.

The current conflict between Venezuela and Guyana stem from territorial claims that the former contends the British Empire stole from the country during the declared independence of Guyana.

The current President of Venezuela, Nicolas Maduro, is demanding that drilling in Guyana stop, because the territory actually belongs to his government. Maduro is under increasing pressure at home, as low oil prices and international sanctions have forced the economy into a tailspin.

According to OPEC statistics, 95% of government revenues are derived from oil production and exportation, and the sector accounts for at least a quarter of total GDP.