Lack of commercial substance: arrangements designed to obtain tax benefits are characterised and their tax effects disregarded. An arrangement lacks commercial substance where its substance differs materially from its form or it includes features such as round trip financing, an accommodating party, offsetting elements, disguised transactions affecting funds, artificial asset or residence location aimed solely at obtaining a tax benefit, or no significant effect on business risks or net cash flows apart from any tax benefit. Round trip financing encompasses series of fund transfers among parties lacking substantial commercial purpose other than tax advantage, regardless of traceability, timing, sequence, or transfer means. Certain factors may be relevant but not determinative, including duration, tax payments, and exit routes.