In the economy occur when it is impossible to increase supply to match an unexpected surge in demand. In boom years, for example, there have been shortages of microchips, forcing producers of a huge range of products to slow down their rate of output. There may also be shortages of skilled labour which make it difficult for firms to hire the kind of people they need in order to expand. Bottlenecks can lead to prices of scarce resources being bid up as buyers compete for them. This can be the start of an acceleration in inflation during a boom.