The present study aims to increase our knowledge of Mandarin lexical tones in fluent speech, more specifically their occurrence frequency distributions and their duration patterns. First, the occurrence frequency of each lexical tone was computed in a large speech corpus (∼ 220 hours). Then the duration of each lexical tone, as well as the impact of word length, syllable position and the prosodic position were investigated. Overall, results show that Tone 3 tends to have the longest duration among all lexical tones. Nonetheless, the factors word length, syllable position and prosodic position are found to impact tone duration. Monosyllabic words exhibit tone durations closer to those of word-final syllables (especially for disyllabic words) than to other syllable positions. Moreover, tone duration tends to be the longest at word's right boundary in Mandarin, regardless of word length. An effect of prosodic position is also found: the duration of Mandarin lexical tones tends to increase with higher prosodic level. Tone durations are the longest in phrasefinal position, followed by word-final position and word-medial position, regardless of the tone nature.