Yes it's typically twice a year. However, I see Quakerstate which is a brand of the same parent company has a rebate for the entire year.
I don't mean to start a oil debate thread, but you may want to wait for your rebates checks to clear the bank before buying more. Pennzoil and Quaker State are hit and miss with their approvals. Denying rebates for what appears to be no reasons.
I don't think there is going to be much of a rebate this year...I see one at Walmart here in Wisconsin...2.5 dollars off of the typical 24.99 price tag. And I see a sale off there 0 w 20 for 17.99 for five quarts.
I by the way did get my 20 dollar rebate check after a month or so...so I effectively got 10 quarts for 30 dollars last year in November.
Menards is another really good spot to stock up for oil. Occasionally you can get a menards rebate check rebate that overlaps a Pennzoil national rebate. That typically gets oil for less than $2.00 per quart.
Menards sells products from Son Paul Menard's NASCAR sponsorship. I believe SOPOS (Shell Oil) is on the way out, with Valvoline and Mobil 1 now being car sponsors.
Most of the Pennzoil and Quaker State is on clearance and gone in most bigger markets. I have yet to see the Valvoline on rebate, but they do have full synthetic Dexron VI for our automatic transmissions at $4.99 per quart. Not bad vs. car part stores.