In most sedimentary basins the overburden pressure increases linearly with depth. In psi/ft, what is the typical gradient?

• A. 0.5
• B. 1
• C. 2
• D. 5

Answer: (B)

The concept being tested is how overburden pressure builds with depth from the weight of rocks above. In sedimentary basins, this lithostatic gradient is set by typical rock densities around 165 lb/ft³. When you convert that weight density to pressure per depth, you get roughly 165 lb/ft² per additional foot, which is about 1.15 psi per foot (165/144 ≈ 1.15). In practice, engineers use a rule of thumb of about 1 psi per foot for overburden. This is higher than the hydrostatic gradient from water, which is about 0.433 psi/ft. So the typical overburden gradient lands near 1 psi/ft.