Ibaka was set to become a free agent following the 2012-13 season, so this extension keeps the Thunder out of any bidding wars to keep Ibaka defending and blocking shots next to Kevin Durant and Russell Westbrook for another four years.
The three Thunder stars will take up around $45-$50 million of the team's salary cap during the three years their contracts overlap. If the NBA salary cap continues to hover around the current $58 million, that doesn't leave a lot of money to fill out the remainder of the roster.
It also doesn't leave the Thunder with many options to re-sign guard James Harden when his contract is up after the 2012-13 season. The reigning NBA sixth man of the year will be a restricted free agent if he is not extended before next summer.