In this paper, the inductances of high-leakage transformers are investigated by analysis, measurement, and finite-element simulation. Series-coupling tests, featuring differential coupling (series opposing) and cumulative coupling (series aiding), are conducted in addition to the standard open-circuit and short-circuit tests. This paper initially reviews and discusses the various test approaches featuring the open-circuit, short-circuit and series-coupling tests. Two very different types of high-leakage transformers are then characterized based on these tests. The short-circuit and series-coupling tests performed comparably for investigating the spatial variations of the primary and secondary leakage inductances of the high-power, high-leakage transformer first investigated. For the second low-power, high-leakage, high-resistance planar transformer the differential-coupling test proves to be a more useful, accurate, and insightful test than the short-circuit test.