The Senate consists of 27 members, 2 per electoral district, and 11 elected according to the different districts proportion of population. Two extra seats are granted in each house to the opposition if necessary to limit any party's control to two thirds. Whenever the minority party elects less than 9 senators, the Constitution of Puerto Rico provides for the enlargement of the body through the recognition of "add-on" senators, who become senators "at-large".