It appears that 90-year-old billionaire Kirk Kerkorian would like to follow his fellow "raider" Carl Icahn into the energy business. Specifically, Kerkorian, through his Tracinda Corp., is making a $1.4 billion tender offer to purchase a 16% stake in San Antonio-based oil refiner Tesoro (NYSE:TSO).

If you do the math, Kerkorian is offering $64 a share for 21.9 million shares of Tesoro. The offer represents an 11.9% premium over the $57.20 share price the day before the offer was announced.

On Monday, Tesoro's board responded to Kerkorian's overture by saying that it would review the offer. And since it hasn't yet issued a clear reaction, that very uncertainty caused the company's shares to slide back to near their pre-offer level on Monday.

Tesoro currently owns seven refineries with a combined capacity near 669,000 barrels of oil a day and operates more than 890 branded retail stations. During the past half-dozen years, Tesoro has spent about $3.4 billion acquiring refineries and service stations. The company's shares have increased in value more than 90% in the past year.

Kerkorian made his original fortune by investing in the entertainment and lodging industry and, more recently, in automobile companies. Last year, he pushed for a General Motors (NYSE:GM) affiliation with overseas auto companies.

In any event, Fools, my takeaway on the investment implications of the offer is this: If you liked Tesoro before Kerkorian stepped up, your mind probably shouldn't have changed. If you were rendered cautious by the run-up in the company's shares and squeezed refinery margins, you similarly shouldn't have altered your opinion. For my money, given those skinnier margins and the imminent return to full operations of a couple of BP (NYSE:BP) units, I'm inclined to be cautious with the refiners for now.

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