Order Imbalance Ratio

The Order Imbalance Ratio (OIR) measures the asymmetry between buy and sell order flow. Defined as buy volume over total volume, it sits at 0.5 when the two sides are balanced; readings above 0.5 mean buy pressure dominates, below 0.5 sell pressure. Persistent imbalance often precedes short-term price moves, which is why it is a staple input in microstructure and execution models.

OIR can be computed at any timescale, from tick-by-tick to intraday windows, and is usually normalized against a rolling baseline so a reading can be judged as high or low for that name. It is most informative in thin markets and around scheduled events, where a given imbalance moves price more than it would in deep, liquid conditions.