Sound power measurements of acoustic sources are generally made in reverberation or anechoic chambers using acoustic pressure measurements as outlined in specific ISO or other standards. A reverberation chamber produces an approximate diffuse-field condition, wherein the sound power is determined from the spatially averaged squared pressure. An anechoic chamber produces an approximate free-field condition, wherein the sound power is estimated from squared pressure over an enveloping measurement surface. However, in many cases it is desirable to estimate sound power within nonideal semi-reverberant spaces. In these environments, both direct and reverberant energies may contribute significantly to the total acoustic field. This paper introduces two measurement methods that utilize a weighted combination of potential and kinetic energy densities, known as generalized acoustic energy density, to estimate sound power in nonideal semi-reverberant rooms. The first method employs a generalized sound power formulation, which is an adaptation to an equation developed in 1948 for semi-reverberant spaces. The second, called the two-point in situ method, is a technique based on the generalized sound power formulation for quick and accurate in situ sound power estimates. Since the generalized acoustic energy density is more spatially uniform than the squared acoustic pressure in an enclosed field, these methods have the advantage of achieving the same accuracy in sound power determination with fewer measurement positions. This thesis explores the possibility of using these new methods in place of methods outlined in current ISO standards by describing analytical, numerical, and experimental results.