Abstract: This paper introduces two innovations in the design of prefix adder carry trees: use of high-valency prefix cells to achieve low logical depth and end-around carry adders with reduced fan-out loading (compared with the carry select and flagged prefix adders). An algorithm for generating parallel prefix carry trees suitable for use in a VLSI synthesis tool is presented with variable parameters including carry tree width, prefix cell valency, and the spacing of repeated carry trees. The area-delay design space is mapped for a 0:25\mu mCMOS technology for a range of adder widths as a comparative study.