The task is especially important for McCain, who would be the oldest candidate ever elected to a first term as president if he wins in November, The New York Times reported Wednesday.

The Times says McCain has directed his campaign staff to study past methods and is particularly interested in finding out "what other processes were used in previous selections of the vice president."

Mentioned as potential running mates are Govs. Tim Pawlenty of Minnesota, Charlie Crist of Florida and Mark Sanford of South Carolina.

Michael Nelson, a Rhodes College political science professor who has written about the vice presidency, told the Times there are three ways McCain could go: He could tap a conservative to reinforce the party's base, select someone with crossover appeal to attract independents or concentrate on geography by picking a running mate from a swing state.