commutative contract

from Bouvier's Law Dictionary, Revised 6th Ed (1856)

COMMUTATIVE CONTRACT, civil law. One in which each of the contracting 
parties gives and, receives an equivalent. The contract of sale is of this 
kind. The seller gives the thing sold, and receives the price, which is the 
equivalent. The buyer gives the price and receives the thing sold, which is 
the equivalent. 
     2. These contracts are usually distributed into four classes, namely; 
Do ut des; Facio ut facias; Facio ut des; Do ut facias. Poth. Obl. n. 13. 
See' Civ. Code of Lo. art. 1761.