The onset of the monsoon season in India usually leads to a drop in sales of petrol and diesel. This can impact the Indian economy in several ways:

• As a major importer of crude oil, a drop in petrol and diesel sales can reduce India's import bill and improve its trade balance
• The drop in demand for fuel can lead to lower prices, which can reduce the cost of production for businesses and eventually translate into lower prices for consumers
• However, it can also lead to lower tax revenues for the government, since fuel taxes are an important source of revenue
• Lower demand for fuel can also have an impact on the stock prices of oil marketing companies and impact the overall sentiment in the equity market
• On the other hand, a good monsoon can lead to higher agricultural output, which can boost rural demand and economic growth, offsetting the impact of lower fuel sales to some extent

Overall, the impact of monsoon on the sales of petrol and diesel and the economy depends on several factors such as the level of oil prices, the tax regime, and the linkages between different sectors of the economy.