The options have come to light in papers submitted by Lasmo to the Securities and Exchange Commission, as part of its defence against the hostile all-paper offer.
The options were granted on 25 April, about two weeks after it launched a pounds 219m rights issue and at a time of intense market rumours that Enterprise was planning a bid.
Beneficiaries of the options include Joe Darby, Lasmo's chief executive, Dick Smernoff, finance director and John Hogan, managing director of its North Sea operations. Between them the trio received about 270,000 options at Lasmo's share price then of 147p. The balance was granted to two other senior managers not on the board.
On 27 April, a day after an approach by the Takeover Panel, Enterprise admitted that it was considering a bid and formally tabled its offer on 28 April.
Although Lasmo shares surged ahead to 169p on the bid rumours, they have since fallen back, closing at 147.5p yesterday.
A Lasmo spokesman said the company had disclosed its intention to grant options in its rights document, although the process was not completed until 25 April.
'Lasmo has been a takeover bid target for ages. The decision to grant options was taken long before the latest speculation about Enterprise began,' he said.