Looking on the internet deeply has found these results:

buy is the most popular phrase on the web.

purchase 11,640,000,000 results on the web	buy 16,670,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Franchise contracts increasingly include purchase options. Unused medicinal products must be returned to the point of purchase. Your clients want the purchase agreement voided. Vehicle purchase financing activities are therefore concentrated in these segments. Those are Robertson's purchase orders. My client arranged the first purchase. Expect delivery of your purchase within a fortnight. Mr Field, you arranged the purchase of Leatherslade Farm?	Money enables you to buy anything. We forgot to buy strawberry milk. My partner proposed to buy some information... College kids, mostly looking to buy beer. Someone used it to buy an amplifier. Somebody else wants to buy your airline. People with money were able to buy butter. You could buy your own thoroughbred.

purchase

11,640,000,000 results on the web

buy

16,670,000,000 results on the web

More popular!

Franchise contracts increasingly include purchase options.
Unused medicinal products must be returned to the point of purchase.
Your clients want the purchase agreement voided.
Vehicle purchase financing activities are therefore concentrated in these segments.
Those are Robertson's purchase orders.
My client arranged the first purchase.
Expect delivery of your purchase within a fortnight.
Mr Field, you arranged the purchase of Leatherslade Farm?