SANTA ANA, CALIF. ? A former Playboy Playmate has caught the eye of oil executives, who fear her battle for half of her late husband’s estate could leave them with a steep tax bill.

Anna Nicole Smith seeks half the fortune of oil tycoon J. Howard Marshall. The bulk of the fortune held by Marshall, who died 14 months after their 1994 wedding, was in Koch Industries stock.

The Wichita, Kan.-based oil conglomerate is the nation’s second-largest privately held company. Marshall held 16 percent of the company, a stake estimated to range in value from $170 million to $1.5 billion.

Smith, 34, claims she is entitled to half that amount, and has waged a six-year legal battle against Marshall’s stepson, E. Pierce Marshall, to prove it.

If Smith prevails in her U.S. District Court case in Santa Ana, she could force a ruling on the value of Koch Industries, a 13,000-worker company with oil, natural gas, refining, petrochemical, agricultural and other holdings.

That could carry estate-tax implications for brothers Charles and David Koch, Koch Industries namesakes, as well as Marshall’s heirs.

The Koch brothers also could be forced to sell some shares in their company to a third party.

The company has sent an attorney to keep tabs on the trial.

A decision on the case is expected this month.