Retailers have become bullish on denim. More and more brands are adding or bulking up their denim lines (recently Tory Burch, Elizabeth and James, Gap, and Rag & Bone) And these expansions are for good reason: Jeans are, more than ever, a constant in most consumers’ wardrobes. Cotton Incorporated, a company funded by the cotton industry, estimated last year that 96% of consumers now own denim—a whopping seven pairs per person on average. Market research firm Mintel forecasts that jean sales in the U.S. will reach $18 billion by 2013.

[Left: Style blogger Rumi Neely in TEXTILE Elizabeth and James flares. Photo via FashionToast. Right: Shopbop fashion director Morgan Wendleborn. Photo via The Sartorialist]

Jeggings, distressed denim, the boyfriend, and ultra-skinny—there’s always a new look because, as the president of Gap has said, “the big opportunity [with denim] is with constant innovation from a fashion perspective.”

The biggest new trend for spring is a return to ‘70s style, with the new go-to shape for jeans the iconic flare. Flare-leg jeans are already selling well at high-end denim labels likeJ Brand. Founder and CEO Jeff Rudes says, “We have seen a huge global demand for the [flared] Love Story jeans and for wider leg openings.”

[J Brand’s “Love Story” bell bottom and “Babe” elephant bell bottom. Photos via J Brand]

The Olsen twins, who launched their denim line, Textile, in March, decided to make their first collection ‘70s-focused. It offers three styles—two of which are flares.

[The Jimi jean and the Stevie jean from Elizabeth and James. Photos via Elizabeth and James]

The flare is available through almost every big brand that sells denim now, and at almost every price point. And we’re sure it will dominate until February, when fashion designers will reveal the next must-have. The real question is, just how long can retailers continue to rely on jeans to boost their bottom lines?