Sentiment analysis and Opinion mining has emerged as a popular and efficient technique for information retrieval and web data analysis. The exponential growth of the user generated content has opened new horizons for research in the field of sentiment analysis. This paper proposes a model for sentiment analysis of movie reviews using a combination of natural language processing and machine learning approaches. Firstly, different data pre-processing schemes are applied on the dataset. Secondly, the behaviour of two classifiers, Naive Bayes and SVM, is investigated in combination with different feature selection schemes to obtain the results for sentiment analysis. Thirdly, the proposed model for sentiment analysis is extended to obtain the results for higher order n-grams.