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<p>Since 1850 the concentration of atmospheric methane (<span class="inline-formula">CH₄</span>), a potent greenhouse gas, has more than doubled. Recent studies suggest that emission inventories may be missing sources and underestimating emissions. To investigate whether offshore oil and gas platforms leak <span class="inline-formula">CH₄</span> during normal operation, we measured <span class="inline-formula">CH₄</span> mole fractions around eight oil and gas production platforms in the North Sea which were neither flaring gas nor offloading oil. We use the measurements from summer 2017, along with meteorological data, in a Gaussian plume model to estimate <span class="inline-formula">CH₄</span> emissions from each platform. We find <span class="inline-formula">CH₄</span> mole fractions of between 11 and 370&thinsp;ppb above background concentrations downwind of the platforms measured, corresponding to a median <span class="inline-formula">CH₄</span> emission of 6.8&thinsp;g&thinsp;<span class="inline-formula">CH₄</span>&thinsp;s<span class="inline-formula">⁻¹</span> for each platform, with a range of 2.9 to 22.3&thinsp;g&thinsp;<span class="inline-formula">CH₄</span>&thinsp;s<span class="inline-formula">⁻¹</span>. When matched to production records, during our measurements individual platforms lost between 0.04&thinsp;% and 1.4&thinsp;% of gas produced with a median loss of 0.23&thinsp;%. When the measured platforms are considered collectively (i.e. the sum of platforms' emission fluxes weighted by the sum of the platforms' production), we estimate the <span class="inline-formula">CH₄</span> loss to be 0.19&thinsp;% of gas production. These estimates are substantially higher than the emissions most recently reported to the National Atmospheric Emission Inventory (NAEI) for total <span class="inline-formula">CH₄</span> loss from United Kingdom platforms in the North Sea. The NAEI reports <span class="inline-formula">CH₄</span> losses from the offshore oil and gas platforms we measured to be 0.13&thinsp;% of gas production, with most of their emissions coming from gas flaring and offshore oil loading, neither of which was taking place at the time of our measurements. All oil and gas platforms we observed were found to leak <span class="inline-formula">CH₄</span> during normal operation, and much of this leakage has not been included in UK emission inventories. Further research is required to accurately determine total <span class="inline-formula">CH₄</span> leakage from all offshore oil and gas operations and to properly include the leakage in national and international emission inventories.</p>