CaptainBlack said: The supply and demand curves are not generally straight lines. In the case of this question at the limiting supply the supply curve is horizontal as no increase in price corresponds to an increase in supply. Click to expand... OK I was thinking the price was the horizontal axis, the curve is vertical at the maximum supply CaptainBlack said: That should be horizontal asymptote at the maximum quantity that can be supplied Click to expand... No I was right first time price is the vertical axis supply the horizontal, the supply curve is vertical at the limiting supply. Increasing price does not then increase supply. So an increase in demand results in increased price but not supply.