My understanding is that the North American crude oil * (continuous product) in ICBC account is not spot but futures, so the average price will change during the extension. For example, although the crude oil in April and the crude oil in May are both crude oil, they are not the same crude oil, so the share will change during the rollover process.

The official explanation of the specific rules I found is as follows:

On the adjustment day of account crude oil continuous product share, ICBC will adjust the account crude oil continuous product share for customers according to the price before and after adjustment. Share adjustment distinguishes between buying before selling and selling after buying, and the total assets of customers remain unchanged before and after share adjustment.

For the transaction of buying before selling, ICBC calculates the customer position after stock adjustment according to the customer position, the price before stock adjustment and the price after stock adjustment, and returns some funds less than 0. 1 barrel to the customer's fund account, that is, the position before stock adjustment × the price before stock adjustment = the position after stock adjustment × the returned funds.

For the transaction of selling before buying, ICBC calculates the customer position after stock adjustment according to the customer position, the price before stock adjustment and the price after stock adjustment, and releases the remaining margin of 0. 1 barrel, that is, the position before stock adjustment × the price before stock adjustment = the position after stock adjustment × the release margin. ICBC will announce the price before and after the adjustment of the continuous product share of crude oil in the account, and customers can make inquiries through online banking, mobile banking and other channels.