Unless we are in some kind of world war situation, it doesn't matter whether it is a US company or a foreign company that increases its reserves. Oil flows in a free market to the market set (OPEC) prices. China being a communist country with state run oil companies is an exception to this situation. If Sinopec increases their "reserves" by purchasing assets or companies, they have some control where that oil goes to and can control the internal price of oil in their country only.
The big US oil companies drill for oil all over the planet and also ship and sell the oil all over the planet. The "US oil reserves" is usually meaning the amount the US Government has stockpiled for government or emergency use. What publically traded oil companies such as Exxon or Chevron have for reserves has nothing to do with US reserves.
I am not too concerned on which foreign oil company "owns" the reserves as long as they are selling it in the open market. IMHO, there should be some concern for what the future holds for communist or socialist countries who are trying to purchase assets for power. These state own oil companies can control the flow of their oil away from the free markets. But, ironically, some state own oil companies such as in Brazil, control way more oil than their countries will ever need and thus require a "free" market to distribute their assets in exchange for the power (money or other political powers) they receive.
Just ramblings….
