Go to the OTCBB site in my last message. The answer to your question is the bid/ask spread. The MMs make their money by selling you shares at the ask, and buying mine (for example) at the bid. They pocket the bid/ask difference.

See the "ask" side of the list? The one on the top of that side is called the "best ask", or the lowest price any MM is asking from you, for you to purchase new stock.

See the "bid" side of the list? The one on the top of that side is called the "best bid", or the highest any MM is willing to pay you, for you to sell your existing stock.

The MM's can and do change positions constantly by changing their individual bid and ask prices. Occasionally, you will put in an order to buy at the ask and it will fill below the ask, occasionally, you will put in an order to sell at the bid, and it will go through slightly higher. This is usually due to the factors Cooky (today I think) explained.