Jon "DRJ" Najarian, co-founder of OptionMonster.

Speculation that UnitedHealth Group ( UNH) is interested in buying Coventry Health Care ( CVH) lifted Coventry's shares as much as 10% today, while driving short-term options buying.

In the trading day's first hour, CVH traded 11,700 calls, most at the April 15 strike, where some 7,400 contracts changed hands. Normal call activity over the past 30 days has been 730 contracts.

At mid-session, Bethesda, Maryland-based Coventry was trading at around $13.10, well outside the money.

UNH, based in Minnetonka, Minnesota, has a market cap of $25.4 billion, substantially greater than Coventry's $1.9 billion.

Last October, CVH lowered its earnings guidance and the shares plummeted to about $18 from a previous close of about $28.

Disclosure: The writer has a position in Coventry Health Care.

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