Proportion extend sort (abbreviated as PESort) is an in-place, comparison-based sorting algorithm which attempts to improve on the performance, particularly the worst-case performance, of quicksort. The basic partitioning operation in quicksort has a linear access pattern which is extremely efficient on modern memory hierarchies, but the performance of the algorithm is critically dependent on the choice of a pivot value. A good pivot will divide the data to be sorted into nearly-equal halves. A poor choice will result in a grossly lopsided division, leaving one part almost as large as the original problem and causing O(n2) performance.