Shifts in demand and supply curves can occur simultaneously and in the same direction.
Consider a market for gasoline cars.
Suppose the economy is thriving. The heightened consumer confidence and income levels boost demand for new cars, shifting the demand curve right.
Concurrently, advancements in manufacturing technology reduce production costs, shifting the supply curve right as well.
The shifts of the demand and supply curves to the right result in an increase in the equilibrium quantity, while the equilibrium price might not change substantially as both supply and demand have increased. The equilibrium price could increase, decrease, or remain constant depending on the magnitude of the shifts in demand and supply.
Conversely, consider an economic recession. The reduced consumer incomes lead to a leftward shift in car demand.
Simultaneously, if production costs rise, manufacturers produce fewer cars, resulting in a leftward shift of the supply curve.
The shifts of the demand and supply curve to the left decrease the equilibrium quantity. Here, the direction of price change depends on the relative magnitudes of the shifts.