Because much of the Isis is too narrow for side-by-side racing, the bumps format was developed. At the beginning of each division, thirteen crews line up front-to-back down the river, with one and a half boat-lengths of clear water between them. When a cannon is fired, the crews start rowing, and each tries to bump the boat in front before being bumped by the boat behind.

There are two sets of bumps races each year, Torpids in Hilary term and Summer Eights in Trinity term. Each set of bumps races consists of four subsequent days of racing. The start order for subsequent days is adjusted to move successful boats up, while boats that were bumped move down. Over the years, boats aspire to reach “head of the river”, first place in the first division. Trophy oars termed “blades” are awarded to boats which successfully bump up at every opportunity on each of the four days of racing without themselves being bumped.

Torpids

Held annually (if river conditions allow!) in the 7th week of Hilary term, Torpids is most novices' first experience of the excitement of bumps racing

In Torpids, a boat that bumps successfully stops rowing, and is safe from itself being bumped. However, the same is not true for a boat that is bumped, and so occasionally crews can be bumped multiple times over the course of a single race.

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Summer Eights

The premiere event on Oxford’s collegiate rowing calendar, Summer Eights takes place each May or June in fifth week of Trinity term. Eights Week traditionally falls under sunny skies, and Blues rowers — that is, those who compete against Cambridge in the Varsity boats — are eligible to row for their colleges. A third difference to Torpids is that both crews involved in a bump stop rowing.