Abstract. Manta is a highly optimizing compiler that translates Java source code to binary executables. In this paper, we discuss four Java-specific code optimizations and their impact on application performance. We assess the execution time of three application kernels, comparing Manta with the IBM JIT 1.3.0, and with C-versions of the codes, compiled with GCC. With all three kernels, Manta generates faster code than the IBM JIT. With two kernels, the Manta versions are even faster than their C counterparts.