BOGOTA, March 1 (Reuters) - Colombian state-run oil company Ecopetrol said its proven oil and gas reserves were down 11 percent in 2015 to 1.85 billion barrels equivalent because of a decline in exploration caused by low crude prices.
The reserves were equivalent to 7.4 years of output, down from 2014 figures of 8.6 years. The reserves' replacement index was 6 percent, Ecopetrol said in a statement late on Monday.
"The largest contributions to reserves come from the Castilla and Chichimene fields, both operated directly by Ecopetrol, and the Rubiales field, which will be operated by the company from June 2016," the statement said.
Ninety-five percent of the proven reserves are the property of Ecopetrol, while the remainder belongs to partners and subsidiaries.
The company had reported 2.08 billion barrels equivalent of reserves in 2014. (Reporting by Luis Jaime Acosta; Writing by Julia Symmes Cobb; Editing by Lisa Von Ahn)