In this work we consider the following class of fractional p&q Laplacian problems (−∆) s p u + (−∆) s q u + V (εx)(|u| p−2 u + |u| q−2 u) = f (u) in R N , where ε > 0 is a parameter, s ∈ (0, 1), 1 < p < q < N s , (−∆) s t , with t ∈ {p, q}, is the fractional t-Laplacian operator, V : R N → R is a continuous potential and f : R → R is a C 1-function with subcritical growth. Applying minimax theorems and the Ljusternik-Schnirelmann theory, we investigate the existence, multiplicity and concentration of nontrivial solutions provided that ε is sufficiently small.