Abstract: An inductive collar locator tool is provided that provides improved sensitivity and precision in locating collars and other discontinuities in a casing string. In a preferred embodiment, the collar locator includes a transmitter coil that produces an oscillating magnetic field, which couples to the casing string proximate the tool. The tool also includes a pair of spaced receiver coils connected to signal processing circuitry which provides an output signal representing the difference in the phase of the magnetic field detected by the receiver coils. The phase difference is relatively constant when the tool is in plain casing pipe, but it changes rapidly when the tool passes through pipe that includes discontinuities, such as joints or collars. The collar locator tool may include an on-board oscillator and digital signaling capabilities. The collar locator is preferably enclosed in a titanium pressure housing that is adapted for through-tubing operations.