Reliability Growth analysis is a process of collecting, modeling, analyzing and interpreting data from the reliability development test program to achieve reliability goal. Many mathematical models have been developed for reliability growth in the literature. In general, it is not possible to fix a priori the model to be used in a given situation. A physical motivation of the problem, based on failure or defect causes/mechanisms, can help in such a choice. The Power Law Process (PLP) is vastly used for monitoring reliability growth during the development test phase. However, in the reliability growth context, the intensity function of the PLP model has two unrealistic situations, viz., it tends to infinity as t tends to zero and tends to zero as t tends to infinity. In this paper, we have proposed Modified PLP model to overcome the second drawback and Doubly Bounded PLP model to overcome both the drawbacks. For the proposed models, the estimates of the model parameters and other quantities of interest have been obtained using Maximum Likelihood approach, for both failure truncated and time truncated data. Reliability Prediction is done using system reliability measures of intensity function and mean time between failures (MTBF). Further confidence intervals of the relevant parameters have been obtained. The procedures developed have been illustrated using numerical examples. Keywords: Bootstrap confidence intervals, maximum likelihood estimation, mean time between failures, non-Homogeneous Poisson Process, test-fix-test program. ______________________________________________________________________ Notations , , parameters. ( ) r t failure intensity at time . t time of failure. th i i t total number of failures. n time of truncation. T additional time-units of testing. S predicted failure intensity at . T S 0 r 2 Cramer-von Mises statistic. n C MLE maximum likelihood estimator. MTBF mean time between failures. NHPP non-homogeneous Poisson process.