The paper determines the number of states in a deterministic finite automaton (DFA) necessary to represent “unambiguous” variants of the union, concatenation, and Kleene star operations on formal languages. For the disjoint union of languages represented by an m-state and an n-state DFA, the state complexity is

$$mn-1$$ ; for the unambiguous concatenation, it is known to be $$m2^{n-1} - 2^{n-2}$$ (Daley et al. “Orthogonal concatenation: Language equations and state complexity”, J. UCS, 2010), and this paper shows that this number of states is necessary already over a binary alphabet; for the unambiguous star, the state complexity function is determined to be $$\frac{3}{8}2^n+1$$ . In the case of a unary alphabet, disjoint union requires up to $$\frac{1}{2}mn$$ states, unambiguous concatenation has state complexity $$m+n-2$$ , and unambiguous star requires $$n-2$$ states in the worst case.