BOGOTA, July 19 (Reuters) - Colombia's Ecopetrol

is in talks with U.S. oil producer Occidental Petroleum ( OXY )

to possibly buy a 30% stake in shale oil producer

CrownRock, in a transaction potentially worth $3.6 billion, the

North American company said on Friday.

Ecopetrol, Colombia's majority state-owned energy company,

said it was in talks with Occidental in a separate statement on

Friday but did not disclose details about the potential size or

value of a stake, saying such decisions were subject to

analysis.

"Occidental and Ecopetrol are engaged in discussions

regarding a structure for Ecopetrol's potential acquisition of

an undivided 30% interest in the CrownRock assets," Occidental

said in an SEC filing.

If the deal goes ahead, Occidental expects the transaction

to be worth approximately $3.6 billion, subject to customary

purchase price adjustments.

If a deal on the transaction is not reached, "Ecopetrol will

have an option to elect for the Rodeo Midland Basin Joint

Venture to acquire the CrownRock assets, resulting in an

indirect ownership by Ecopetrol of an undivided 49% interest in

the CrownRock assets," the filing said.

Occidental moved to buy shale oil producer CrownRock in

December in a $12 billion cash-and-stock deal, which included

debt.

In May, Occidental reaffirmed its plans to sell $4.5 billion

to $6 billion of assets within 18 months of closing the

CrownRock purchase, which it said could be completed by August.

Shale oil and gas production is highly controversial in

Colombia, where the government of leftist President Gustavo

Petro is pushing for an outright ban on fracking, much to the

chagrin of factors in the country's energy industry.

Despite this, Ecopetrol - Colombia's largest company - has

shale operations in the U.S. Permian basin.

Occidental expects to use any proceeds from a deal with

Ecopetrol to pay down a portion of its term loans, the U.S.

company said.