As Covid-19 struck, quarantines were imposed, aeroplanes were grounded and the skies emptied.
On 13 March 2020, the US banned entry to non citizens coming from Europe; a couple of weeks later, California became the first state to issue a stay-at-home order. By the end of April, 41 other states had followed suit. The impact on the airline industry in the US was dramatic and can be seen in the plunge in fuel usage of US airline companies as compared to the same month in 2019: first on international flights, then internal domestic flights. Covid-blighted 2020 burnt only half of the fuel that was used in 2019, and the lowest amount since 1980. With demand drying up, the markets followed, and the price of fuel collapsed to a low of $1 per gallon.
But from the nadir of May 2020, things began to improve. Stay at home orders began to be lifted and domestic travel picked up again, even if at a fraction of pre-Covid levels (the graphic, of course, hides the number of half-empty flights). The return of international travel was steadier, and remains at the whim of restrictions in other countries. At around the same time, the price per gallon began to take off too.