A subsemigroup S of a semigroup Q is a left order in Q, and Q is a semigroup of left quotients of S, if every element of Q can be written as a−1b for some a, b∈S with a belonging to a group scriptH‐class of Q. Necessary and sufficient conditions on a semigroup S are obtained in order that S be a left order in a completely 0‐simple semigroup Q. The class of all completely 0‐simple semigroups of left quotients of S is related to the set of certain left congruences on S. Axioms are provided for semigroups which occur in the discussion of left orders in completely 0‐simple semigroups.