We design a variation of skip lists that performs well for generally biased access sequences. Given n items, each with a positive weight w _i, 1≤ i ≤ n, the time to access item i is O (1 + log W/w _i), where W = Σ_i=1ⁿ w _i; the data structure is dynamic. We present deterministic and randomized variations, which are nearly identical; the deterministic one simply ensures the balance condition that the randomized one achieves probabilistically. We use the same method to analyze both.