PricewaterhouseCoopers tabulates the votes and the final list of nominees is announced in January. Another round of secret voting takes place, with members of the Academy only able to vote on the final nominees listed in each category. Those ballots must be returned to PricewaterhouseCoopers before the specified deadline. After the ballots are tabulated, only two partners of PricewaterhouseCoopers will know the results until the envelopes are opened on stage during the Academy Awards presentation.
In August 2009 the Academy changed the voting process for the Best Picture category. After increasing the number of nominees in the Best Picture category from 5 to 10, the Academy opted for a preferential voting system to determine the winner of the Best Picture Oscar. Instead of merely making a check mark next to their favorite film, Academy voters will number the 10 nominees from 1 to 10 with 1 being their first choice, etc.
SOURCE: The Academy of Motion Picture Arts and Sciences