High-resolution seismic-reflection data were collected across the upper- and middle-continental slope of the northern Gulf of Mexico to study the distribution of gas and gas hydrate and their relation to seafloor slides. Seafloor gas vents and gas hydrate are widely reported near salt-related structures, but gas hydrate is only reported in one deep drill site. In our study area, the upper 1000 m subbottom, which includes the gas-hydrate-stability zone (GHSZ), has many high-reflectivity zones (HRZs) that lie at varied subbottom depths near shallow diapirs, faults and likely debris flows, and that are interbedded within layered sedimentary sections. HRZs occur near seafloor gas vents and along faults, lie below (more common) and within the GHSZ, and coincide with zones of shallow water-flows. Bottom simulating reflections are rare in the Gulf, and not seen in our data. We believe HRZs result largely from free gas in sandy beds. These beds would also contain hydrates within the GHSZ. We estimate base GHSZ for methane and two petrogenic gases, and on seismic sections the base GHSZ correlates reasonably with top of HRZs in some thick well-layered basin sections, but poorly where shallow sediments are thin and strongly deformed. The correlation is equivocal in part because the values used to calculate estimates of base GHSZ are poorly constrained and may vary widely, especially near areas of large water- and sediment-flows. HRZs may be a potential indicator for nearby gas hydrate. HRZs also lie at the base of at least two large seafloor slides (e.g., up to 250 sq. km.) that may be actively moving along decollement faults that sole within the GHSZ or close to the estimated base of the GHSZ. We suspect that water/gas flow along these faults and adjacent strata provide gas to source gas hydrate in the GHSZ, and flow weakens sediments that slide on salt oversteepened slopes when triggered by earthquakes.