In this paper, we propose a social game to promote efficient driving and provide feedback to the user. The proposed system uses a fuzzy logic system in order to assess the driving style from the point of view of the fuel consumption. The output is a score between 0 (not efficient) and 10 (efficient). This value can be compared with the score from other users of the social network that have similar characteristics in order to do a fair comparison and obtain eco-driving advice adapted to the environment (e.g., braking frequency is greater on urban road than highway). Providing feedback to the user is essential in driving eco-systems for changing bad driving habits and not returning back to driving bad-habits. In our case, the system provides two types of feedback. The first type of feedback is provided in real time. When the user does not comply with any of a preconfigured set of eco-driving rules, he gets a warning message. The second type of feedback is based on a calculated relative score for each user according to his or her driving style, positioning the user into a ranking of eco-driving users and generating a set of eco-driving tips.