In understanding the market supply curve, it's essential to differentiate between the short run and the long run. In the short run, the number of firms in the market remains fixed, which means that the market supply curve is derived from the individual firms' marginal cost curves. Each firm's marginal cost curve effectively acts as its supply curve when prices exceed the average variable cost.

For instance, consider an individual firm with a marginal cost curve that is upward sloping. If this firm supplies 100 units at a price of $5 and 200 units at a price of $10, we can extend this to a hypothetical market scenario with 1,000 identical firms. By summing the quantities supplied by each firm at various price points, we can determine the total market supply. At a price of $5, for example, the market supply would be 100,000 units (100 units from each firm multiplied by 1,000 firms).

This process of aggregating individual supply curves to form the market supply curve is straightforward and mirrors the principles of supply and demand previously studied. The key takeaway is that the market supply curve in the short run is simply the horizontal summation of all individual firms' marginal cost curves at each price level.

As we transition to the long run, the dynamics of the market supply curve become more complex, involving factors such as entry and exit of firms, which will be explored further in subsequent discussions.