Acoustic impedance (AI) is correlated with total organic carbon (TOC), where AI decreases as TOC increases. An example is presented that demonstrates this relationship using wireline and lab data for a source rock from northwest Saudi Arabia. We discuss why this relationship is expected and support this expectation quantitatively with a simple, theoretical rock-physics model (not calibrated to any data). We then use well and lab data to establish an empirical relation and combine it with seismic data to map the areal distribution of TOC over our study area. We verify quantitatively that the addition of seismic data improved the map. Finally, we discuss various issues regarding the confidence that can be attributed to such a map.