Arm's length pricing under transfer pricing rules depends on prescribed methods, comparability factors, and current-year data use. Arm's length price for an international transaction or specified domestic transaction is determined by the most appropriate prescribed method, including comparable uncontrolled price, resale price, cost plus, profit split, transactional net margin, or any other method under rule 78. Comparability is assessed by the characteristics of the property or services, functions performed, assets employed, risks assumed, contractual terms, and market conditions. An uncontrolled transaction is comparable where material differences do not affect price, cost, or profit, or can be accurately adjusted. Current-year data is generally used, subject to the specified exceptions for resale price, cost plus, and transactional net margin methods.