Bottom Line has shopped an expanded list of groceries three times since last September. Each time, Wal-Mart was the clear-cut winner over the other three major grocers in the Rochester area — Wegmans Food Markets Inc., Martin's Super Food Store and Tops Friendly Markets.

Across the nation, the world's largest retailer, which has morphed into a grocery powerhouse with its Supercenter concept, isn't going to let anyone beat it on price alone.

Consider Tide laundry detergent.

In September 2005, Wal-Mart's price for a 100-ounce liquid jug was $5.99, tying it for lowest price with Wegmans and Martin's.

In December, Wal-Mart actually finished third at $7.44 a jug, well higher than Wegmans ($5.99) and Martin's ($6.29) and barely below Tops ($7.69).

But in our most recent price check last Tuesday, the Wal-Mart Supercenter in Henrietta had Tide at $5 a jug, cheaper by nearly a dollar than Wegmans. Martin's was $6.29 and Tops $8.21.

Wal-Mart also had the lowest price — albeit only by a few cents in several instances — in 14 of the 15 core sample items on our total list of 58 products. Wegmans was lowest in skinless, boneless fresh chicken breasts at $1.99 a pound, with Wal-Mart second at $2.82.

The shopping list for last week was two items short of December 2005 and three short of September 2005. That's because some items were either not available because of the season — fresh corn on the cob for instance — while others were discontinued by one or more of the grocers. In the first two expanded surveys, the order from lowest prices to highest was identical — Wal-Mart, Martin's, Wegmans and Tops.

This time, Wegmans slipped past Martin's into second lowest, $129.43 to $133.44. Wal-Mart's $113.15 was 12.6 percent below Wegmans, the biggest spread between first and second so far. In September, Wal-Mart's prices were only 2.9 percent lower than Martin's and in December, they were 7.1 percent lower than Martin's.

Among our 15 core items, the largest percentage price growth since September was in a 10.75 ounce can of Campbell's chicken noodle soup. In September, the average price among the four stores was 55 cents. Last week it was 80 cents, a 45 percent hike.

Eggs showed a healthy decline, from an average of 95 cents in September to 69 cents last week. That's a drop of 31 percent.