Well completions, either cased hole gravel packed or cased hole frac packed, often suffer significant productivity decline during hydrocarbon production. In these completions, the perforations are intended to be packed with gravel or proppant, which provides the necessary support to prevent perforation failure and sand production. Ideally, the entire perforation volume is packed with proppant. However, there are cases of poor proppant packing jobs, which may leave perforations partially or completely unsupported. This increases the chances of perforation failure, sand production, and productivity decline. The effect of proppant packing efficiency, i.e., the fraction of perforation volume filled, on productivity decline was investigated in hollow cylinder sand production tests on two different types of sandstone. The experimental results show that lower packing efficiency may lead to earlier perforation failure but does not necessarily cause a significantly larger productivity decline. Different productivity decline mechanisms are also demonstrated with varying packing efficiencies and sandstone types.