Electromagnetic crosstalk poses a serious problem within today's advanced serial communication modules. A major detrimental effect is the degradation of receiver sensitivity in the presence of crosstalk noise. The mitigation of crosstalk penalty becomes increasingly more challenging as data rates increase for higher throughput, as module sizes shrink for increased port density, and as supply rails are reduced for lower power dissipation. In this article, we explore a method for quantifying crosstalk penalty by observing a receiver's bit-error-ratio (BER) versus the phase difference between the transmitted and received signals. This article also presents actual crosstalk measurement results of three different communication module examples.