Among other things we show that for each n-tuple of positive rational numbers (a 1 , . . . , a n ) there are sets of primes S of arbitrarily large cardinality s such that the solutions of the equation a 1 x 1 +• • •+a n x n = 1 with x 1 , . . . , x n S-units are not contained in fewer than exp((4 + o(1))s 1/2 (log s) −1/2 ) proper linear subspaces of C n . This generalizes a result of Erdős, Stewart and Tijdeman [7] for S-unit equations in two variables. Further, we prove that for any algebraic number field K of degree n, any integer m with 1 ≤ m < n, and any sufficiently large s there are integers