The study has two main aims. The first is theoretical and the second methodological. Theoretically, the study seeks to investigate the nature and extent of variation in interlanguage with the aim of identifying and assessing the extent to which factors such as discourse mode (e.g. narrative vs descriptive) and linguistic context are likely to result in variable interlanguage performance. Methodologically, the study seeks to highlight the problems of eliciting valid interlanguage data using the concept of planning as is currently formulated by Ochs (1979) and Ellis (1987). Although interlanguage performance may be shown to be variable it still remains important to assess how widespread variation is in interlanguage, because variation is likely to shed much more light on interlanguage development and use, if it is demonstrated that it is neither restricted to specific structural areas nor typical of learners at particular stages of interlanguage development. With this in mind this study investigates the performance of second language learners at three different levels of proficiency in two linguistic areas - spatial and directional prepositions and the 3rd person singular. Variation in interlanguage has been attributed to a large number of factors some of which are enumerated below - discourse mode, varying planning conditions, topic, setting, interlocutor, linguistic context etc.