This study was an examination of the relationship of lexical richness to the quality of English as a second language (ESL) learners' oral narratives. A computational system was designed to automate the measurement of 3 dimensions of lexical richness, that is, lexical density, sophistication, and variation, using 25 different metrics proposed in the language acquisition literature. This system was used to analyze large-scale data from the Spoken English Corpus of Chinese Learners (Wen, Wang, & Liang, 2005) together with the vocd utility of the Computerized Language Analysis programs (MacWhinney, 2000), which offers an additional measure of lexical variation, the D measure (Malvern, Richards, Chipere, & Duran, 2004; McKee, Malvern, & Richards, 2000). This comprehensive analysis allowed us to identify measures that correlate strongly with the raters' judgments of the quality of ESL learners' oral narratives, as well as to understand the relationships among these measures. This research provides ESL teachers and researchers with a robust tool for assessing the lexical richness of ESL language samples and insights into how lexical richness measures may be effectively used as indices of the quality of ESL learners' speaking task performance. (Contains 7 notes, 1 figure and 16 tables.)