Gas prices fluctuate — meaning, in a tank half-empty sense, they rise — even in a recession, and it just makes sense to look for the cheapest stuff around. (Unless you believe cheap gas degrades your car’s engine, in which case you should continue buying at big chain stations.) Here are five places to go for the cheapest product, most of which actually take you into Somerville.

Cumberland Farms Address: 701 Somerville Ave., Somerville MA 02143 Phone: (617) 776-3596 Hours: 6 a.m. to midnight, seven days a week Owner: The New England-based company Not just gas: Full-service minimart Notes: This Cumby is kept on its competitive toes by the Petrola station a couple of blocks away, occasionally bumping by a penny or two before falling back in line. Same price, cash or credit. Self-service.

Cumberland Farms | Address: 701 Somerville Ave., Somerville MA 02143 | Phone: (617) 776-3596 | Hours: 6 a.m. to midnight, seven days a week | Owner: The New England-based company | At the pumps: Same price, cash or credit. Self-service. | Not just gas: Full-service minimart | Notes: This Cumby is kept on its competitive toes by the Petrola station a couple of blocks away, occasionally bumping by a penny or two before falling back in line.

Hess (Inman Square) Address: 287 Prospect St., Cambridge MA 02139 Phone: (617) 354-9613 Hours: 24 hours, seven days a week Owner: Company At the pumps: Self-service; same price, cash or credit Not just gas: Free air; some snacks; by a 24-hour 7-Eleven Notes: As one of Cambridge’s two 24-hour gas stations (the other being a Shell station on Memorial Drive), Inman’s Hess could be forgiven slightly higher prices — and there are fairly frequent price bounces, so unless you need gas when other stations are closed, be aware you’re gambling. Historically, though, Hess has surprised by matching other lower-price pumps in the area.

Hess (Inman Square) | Address: 287 Prospect St., Cambridge MA 02139 | Phone: (617) 354-9613 Hours: 24 hours, seven days a week | Owner: Company | At the pumps: Self-service; same price, cash or credit | Not just gas: Free air; some snacks; by a 24-hour 7-Eleven | Notes: As one of Cambridge’s two 24-hour gas stations (the other being a Shell station on Memorial Drive), Inman’s Hess could be forgiven slightly higher prices — and there are fairly frequent price bounces, so unless you need gas when other stations are closed, be aware you’re gambling. Historically, though, Hess has surprised by matching other lower-price pumps in the area.

Hess (Porter Square) Address: 2055 Massachusetts Ave., Cambridge MA 02140 Phone: (617) Hours: 6 a.m. to midnight, seven days a week. Owner: Company At the pumps: Self-service; same price, cash or credit Not just gas: Free air; full service minimart; bathrooms Notes: This was the replacement for the notorious Gas With a Smile, welcomed only after it agreed to retain its Zipcar spaces in perpetuity. Like its Inman Square sibling, this Hess can unexpectedly break from the low-prices pack and charge, well, like a chain before crashing back to a price floor.

Hess (Porter Square) | Address: 2055 Massachusetts Ave., Cambridge MA 02140 | Phone: (617) Hours: 6 a.m. to midnight, seven days a week. | Owner: Company | At the pumps: Self-service; same price, cash or credit | Not just gas: Free air; full service minimart; bathrooms | Notes: This was the replacement for the notorious Gas With a Smile, welcomed only after it agreed to retain its Zipcar spaces in perpetuity. Like its Inman Square sibling, this Hess can unexpectedly break from the low-prices pack and charge, well, like a chain before crashing back to a price floor.

Petrola / Aris Auto Address: 675 Somerville Ave., Somerville MA 02143 Phone: (617) 776-9247 Hours: 6 a.m. to 10 p.m. Monday through Saturday, 6 a.m. to 9 p.m. Sunday Owner: George Varelis At the pumps: Full-service; gas is cheaper bought with cash Not just gas: Auto shop; state inspections Notes: Low prices here tend to keep rates low at the neighboring Cumberland Farm. Distributors compete to provide gas, and “we buy from the cheap company,” explains Aris number cruncher Elboukhari Reda. “We balance price and quality and get a good return.”

Petrola / Aris Auto | Address: 675 Somerville Ave., Somerville MA 02143 | Phone: (617) 776-9247 | Hours: 6 a.m. to 10 p.m. Monday through Saturday, 6 a.m. to 9 p.m. Sunday | Owner: George Varelis | At the pumps: Full-service; gas is cheaper bought with cash | Not just gas: Auto shop; state inspections | Notes: Low prices here tend to keep rates low at the neighboring Cumberland Farms. Distributors compete to provide gas, and “we buy from the cheap company,” explains Aris number cruncher Elboukhari Reda. “We balance price and quality and get a good return.”

Address: 73 Summer St., Somerville MA 02143 Phone: (617) 776-6667. Hours: 7 a.m. to 9 p.m. seven days a week.  Owner: Mirian Samayoa At the pumps: Full-service; same price, cash or credit Not just gas: Auto shop; state inspections. Notes: AL Prime is a bit out of the way for many in Cambridge — all the way down by Union Square, in fact — but its prices tend to be consistently among the lowest. Samayoa credits the size of the New England-based “huge company.”

AL Prime Energy / Somerville Gas & Auto Repair | Address: 73 Summer St., Somerville MA 02143 | Phone: (617) 776-6667. | Hours: 7 a.m. to 9 p.m. seven days a week. | Owner: Mirian Samayoa | At the pumps: Full-service; same price, cash or credit | Not just gas: Auto shop; state inspections. | Notes: AL Prime is a bit out of the way for many in Cambridge — all the way down by Union Square, in fact — but its prices tend to be consistently among the lowest. Samayoa credits the size of the New England-based “huge company.”