* About 97,000 acres on the market
* Highest price seen at $25,000 per acre -analyst
* Marathon shedding "non-core" assets
By Anna Driver
HOUSTON, Oct 15 (Reuters) - Marathon Oil Corp is selling a large portion of its undeveloped oil and gas acreage in the Eagle Ford basin in south Texas as the U.S. oil and gas company sheds properties it no longer considers essential to its exploration plans.
Marathon has spent heavily in recent years to acquire oil and gas properties in the Eagle Ford in a strategy aimed at growing production of crude oil and pricier natural gas liquids.
Houston-based Marathon, which has 325,000 acres in the Eagle Ford, is selling about 97,000 acres in Wilson, Karnes and Bee Counties, according to a marketing brochure from the Oil and Gas Asset Clearinghouse, its adviser on the sale.
About of those 200,000 acres are considered "core," or having the best potential by Marathon. The planned sale will not affect the company's core acreage, strategy or production targets, a spokeswoman said.
"No question, this asset is a priority for us, and our investment reflects that - over the next five years - we plan to spend approximately $1.6 billion annually to grow this asset," Dave Roberts, Marathon's head of exploration said in a speech on Monday in San Antonio.
During its second-quarter earnings call, Marathon said its oil and gas output in the Eagle Ford rose 50 percent from the prior quarter, and it is on track to produce an average of 30,000 barrels of oil equivalent per day in 2012.
Valuations in the Eagle Ford have remained high as oil companies and financial firms seek exposure to the light sweet crude produced from rocks in the basin that stretches into Mexico.
Private equity firm KKR & Co LP in July agreed to pay $25,000 per acre for a one-third stake in Comstock Resources' undeveloped Eagle Ford acreage.
Marathon's properties may fetch as much as $25,000 per acre, with the low end seen at $15,000, according to Allen Good, oil analyst with Morningstar in Chicago.
In May, Marathon bought privately held Paloma Partners II LLC for $750 million. At the time, Paloma owned about 17,000 acres and production of about 7,000 barrels of oil equivalent per day. In 2011, it paid nearly $25,000 per acre to acquire 141,000 acres from privately held Hilcorp.
Bids on the properties are due Oct. 25.