The concept of a series of related transactions arises in transfer pricing and international tax law when two or more transactions between associated enterprises, or between a taxpayer and third parties operating in concert, are so closely connected that they cannot be evaluated reliably in isolation. Rather than applying the arm’s length standard to each transaction individually, the analytical question becomes whether the transactions must be assessed as a single economic arrangement. This principle draws authority from Article 9 of the OECD Model Tax Convention, which requires that conditions between associated enterprises reflect those that would prevail between independent parties, and from domestic anti-avoidance provisions such as Canada’s General Anti-Avoidance Rule under section 245 of the Income Tax Act and Norway’s non-statutory anti-avoidance doctrine.

Disputes arise when a taxpayer structures an arrangement across multiple steps to achieve an outcome that, viewed in its entirety, produces a tax advantage unavailable if the steps were treated as a unified transaction. Tax authorities typically argue that the series must be collapsed and re-characterised, alleging that intervening steps lack commercial substance. In IKEA Handel og Eiendom AS, the Norwegian Supreme Court upheld denial of interest deductions on an inter-company loan created through a multi-step restructuring. In Deans Knight, Canada’s Supreme Court applied GAAR to a sequence of transactions designed to preserve loss utilisation rights. Conversely, in Medingo, the Israeli District Court found that three post-acquisition service agreements, though related, were commercially genuine when examined individually.

OECD Transfer Pricing Guidelines Chapter I, paragraphs 1.36 through 1.38, address the aggregation of transactions, permitting combined evaluation where transactions are so closely linked or continuous that they cannot be assessed separately on a reliable basis. Chapter III, paragraphs 3.9 through 3.12, address selection of the tested transaction and permit grouping where this produces a more reliable arm’s length measure. The Heidelberg Cement case illustrates this directly: the taxpayer applied TNMM across combined transactions, while the Indian authorities sought transaction-by-transaction analysis, a dispute squarely governed by these paragraphs.

Courts examine whether the individual steps have independent economic substance, whether each transaction was priced on terms an independent party would accept, and whether the overall structure was pre-planned to achieve a tax result rather than a commercial purpose. Evidence of timing, contractual interdependence, absence of third-party risk, and the identity of those who designed the arrangement all bear on the analysis. The burden of demonstrating commercial rationale typically falls on the taxpayer once the authority identifies a structured sequence.

Cases in this category are essential reading for practitioners advising on group restructurings, stepped acquisitions, and financing arrangements, as they define the limits of transactional disaggregation and the conditions under which tax authorities may recharacterise a sequence as a single taxable event.