This document summarizes a project to reduce fraudulent card transactions for a US national bank. An ensemble technique using logistic regression and K-nearest neighbors was developed to classify transactions as fraudulent or legitimate in real time. The project was estimated to reduce fraudulent losses by $16-18 million while costing $4.2 million to develop. Testing on 1 year of transaction data accurately classified transactions and reduced fraudulent cases by 80-90%, saving the bank $16 million.