This document discusses methods for detecting fraudulent transactions from online credit card transactions. It first reviews several existing algorithms for fraud detection from literature, including neural networks, rule induction, case-based reasoning and others. It then discusses selecting important attributes from a credit card transaction dataset containing 20 attributes related to transactions and cardholders. Several attribute selection techniques are applied to identify the most important attributes. Finally, various machine learning algorithms including AdaBoost, logistic regression, J48 and naive Bayes are tested on the dataset to identify the best algorithm for detecting fraudulent transactions, with the document concluding that AdaBoost performs best.