The paper is concerned with evaluating the performance of a 16-ary quadrature amplitude modulation (QAM) signaling when transmitted through a land mobile satellite channel. The channel exhibits fading and shadowing as well as additive white Gaussian noise. Fading and shadowing cause both envelope and phase variations of the received signal. The paper derives upper bounds of the probability of error due to each one of these variations. An expression of the irreducible probability of error is also derived. The derived expressions are useful for the design of land mobile satellite data communication systems.