The Oscars are using a preferential voting system this year to determine the best picture winner. Although attempting to understand the system can sometimes feel a little like trying to divine the secrets of cold fusion, the system is actually logical -- sort of.
Whereas all other categories will use the same system used in the past -- every voter gets to pick one of the five nominees, and the nominee with the most votes wins -- the 10-nominee best-picture category will function differently.
Voters will be asked to rank their best-picture choices from 1 to 10 (though they are not required to complete the ballot in full). Then the academy will gather the ballots and separate them in piles according to voters' first choices. Each movie gets its own pile -- the film that appears most frequently as a first-place choice will naturally have the largest stack, the movie with the next-most first-place votes will have the second-largest, and so forth. Then each stack is counted.
If one film has more than 50% of the votes on the first round (unlikely), it will be declared the winner. If it doesn't, the academy will take the shortest stack -- the movie that got the fewest first-place votes -- eliminate it from contention, remove its stack from the table and redistribute those voters' second choices to all the other stacks.