Who owns Malaysian petrol and who controls the price of petrols?

PETRONAS, also known as Petroliam Nasional Bhd, is Malaysia’s national petroleum corporation. Since its inception in 1974, PETRONAS has grown rapidly to become an integrated oil and gas company with business interests in 31 countries.
It is wholly-owned by the Malaysian Government and is entrusted with the responsibility of developing the oil and gas resources. The [...]

Why does a company’s stock price generally go up on a good announcement, then retreats days after?

I understand that many institutional investors buy lots of shares the day a company announces good news. Usually, the next day, the stock price retreats a little, only to eventually go back up. Why does this happen?