Models of fatigue crack growth rates for medium and low sulfur ferritic pressure vessel steels in pressurized water reactor (PWR) primary environments are developed based on a recent collection of UK data and the EPRI Database for Environmentally Assisted Cracking (EDEAC). The combined UK and EDEAC database contains a broader range of experimental conditions specific to PWRs than either database by itself. Both probabilistic and conventional crack growth rate models are developed that reduce unnecessary conservatism for medium and low sulfur PWR primary water applications and eliminate the explicit dependence on rise time that caused difficulties applying prior models.Copyright © 2003 by ASME