Oral performance in a second language (L2) can be measured in terms of complexity, accuracy and fluency, thus offering an overview of L2 learning. Focusing on the cognitive development of L2 learning, particularly from the point of view of Processing Theory and the Speech Production Model, limited attentional resources hinder simultaneous attention to the variables studied, namely: Performance components of complexity, accuracy and fluency in semi spontaneous oral monologues at different levels of English proficiency (A2, B2 and C1). Complexity was measured in terms of lexical range (as D score, best fit for lexical range) and grammatical complexity (as the average length of words in each clause, and number of clauses in each Analysis of Speech (AS) unit). Accuracy was measured as the proportion of AS units free from errors and percentage of error-free clauses. Fluency was measured by calculating the phonation-time ratio and the mean length of pauses. Regarding trends in L2 language development, results showed increase in all variables across all levels of proficiency. Besides, the variables studied are interconnected within each group sampled. Correlation analysis showed significant correlations between subcomponents within each construct, which suggests that any specific variable of each construct could represent the general state of the components of oral performance.