There is a reason why Mariano Rivera has not accepted the Yankees' offer of a three-year, $45-million contract.
Rivera, according to major-league sources, wants a fourth guaranteed year. The Yankees remain the overwhelming favorite to retain Rivera. No other club is expected to even approach their proposal, much less top it.
But Rivera, who turns 38 on Nov. 29, has instructed his agents to shop him, in part because he was angered by Hank Steinbrenner referring to his age in recent comments about the Yankees' offer, a source says.
Rivera has specifically mentioned following Joe Torre to the Dodgers, and his agents also are contacting other clubs about his availability.
Rivera, sources say, believes he deserves the same length of contract as Yankees catcher Jorge Posada, who is on the verge of re-signing for $52.4 million over four years, and Mets closer Billy Wagner, who received $43 million over four years after the 2005 season.
Posada and Wagner are both 36, nearly two years younger than Rivera — and Wagner was 34 when he signed with the Mets as a free agent.
Rivera also is certain to note that third baseman Alex Rodriguez would be 42 at the end of his proposed 10-year contract with the Yankees — the same age that Rivera would be at the conclusion of a four-year deal.
Rivera's ERA rose to 3.15 last season after four straight years below 2.00, but he went 30-for-34 in save opportunities, regained his dominance in September and worked 4 2/3 scoreless innings against the Indians in the postseason.
