People can reach all kinds of information online incuding reviews and comments on products, movies, holiday destinations and so on. However, one usually need to go through the reviews to have an objective opinion the positive and the negative aspects of the item reviewed. We aim to provie a method that will extract positive and negative opinions on a specific aspect and compare them in an attempt to ease on the information overflow. Contrastive opinion summarization (COS) aims to solve this issue. COS methods extract representative and comparative sentences in terms of specific aspects of a product. In this paper, we propose a new COS method, namely Contrastive Max-Sum Opinion Summarization (CMSOS). This method considers representativeness and contrastiveness at the same time. For the evaluation, we use an English dataset which was specifically created for COS studies. In addition, we created a new dataset in Turkish and shared it publicly. We provide the results on both datasets with our method.