The Xenimus Market Index (XMI) tracks the relative cost of a basket of commonly traded items — analogous to a stock market index.

Each day the geometric mean unit price of each item is computed from the past 24 h of auction listings. The index chains daily: it moves up or down by the same percentage as the basket's average price. The value is expressed in in-game currency — if the XMI reads 3g 50s, that is the geometric mean price of a basket item today.