Texaco may owe Louisiana a $250-million bill.

The attorney general of Louisiana said Texaco underpaid royalties by that amount on natural gas produced from state-owned lands dating to 1973, when the price of gas began to soar. Texaco paid royalties after 1973 based on gas values established in long-term, low-price contracts, and says it owes the state nothing. Louisiana argues that the royalties should have been based on the market value of the gas at the time it was sold. Atty. Gen. William J. Guste Jr. said he expects to present the finding to the State Mineral Board.