Art collectors Keith and Katherine Sachs, who have amassed one of the finest collections of contemporary work in the country, will donate the vast majority of it to the Philadelphia Museum of Art, transporting that institution into the front ranks of large museums with holdings of late-20th and early 21st-century art.

Museum director Timothy Rub called the gift of 97 works, to be announced Friday, transformational and placed it among the three greatest the museum has ever received.

"I'm delighted," Rub said in an interview. "This is an extraordinarily interesting and generous and thoughtful gift to the museum - a wonderful game-changer for us. So I'm as pleased as can be."

The Sachs collection, consisting of about 100 works, is rich in modern masters - Jasper Johns, Ellsworth Kelly - and has a strong core of such minimalist artists as Carl Andre and Donald Judd.

Britain is well-represented, particularly in oil-on-wood paintings by Howard Hodgkin. German artists such as Joseph Beuys and Anselm Kiefer are prominent. And Americans Tony Smith, Sol LeWitt, Brice Marden, Dan Flavin, Kiki Smith, Louise Bourgeois, and Jonathan Borofsky are represented by strong works.

The collection has a particularly prominent sculpture component, including stark outdoor pieces by Richard Serra and Scott Burton, and instantly recognizable work by John Chamberlain, Tony Smith, and Joel Shapiro.

There are large photographs by Jeff Wall and video pieces by Bill Viola.

"A really exceptional strength of the collection is Keith and Kathy's commitment to artists like Ellsworth Kelly, Jasper Johns, and Howard Hodgkin," Rub said. "In some cases, certainly the first two I mentioned, we already have a very fine collection of their work. With the addition of works in the Sachs collection, these become great, great areas of depth for us, and that's really important. We think Kelly and Johns are exceptionally important artists and also central to the story of contemporary art both in this country and internationally."

In other instances, however, the museum lacks strength, Rub noted. "The Sachses have collected artists who we've not been able to acquire. Their collection fills significant gaps in ours and complements ours in significant ways."

Works by Hodgkin and American painter Robert Ryman, video works, and large-scale photography are examples, Rub said.

Four works from the collection already have been placed on view in the modern and contemporary galleries, museum officials said. Jasper Johns' bronze 0-9 (2008) is in Gallery 171, and his oil and encaustic 5 Postcards (2011) is in Gallery 182. Ellsworth Kelly's Cutout in Wood (1950) has been placed in Gallery 175 in context with the artist's early Paris works. In addition, Das Erdtelephon (The Earth Telephone), a mixed-media sculpture by Beuys, can be seen in Gallery 170.

Carlos Basualdo, museum curator of contemporary art (whose curatorial position has been endowed by the Sachses), called the collection remarkable.

"It contains stellar works that reflect some of the most daring and productive directions in contemporary art over the past few decades, [and] it reflects a vision that is deeply personal and grounded in Keith and Kathy's heartfelt affection and admiration for the artists whose work they collect."

The heart of the Sachs collection can be found in its careful attention to minimalist work.

"We always felt there was a certain principle to the way we collect, a certain voice to the collection," Katherine Sachs, 66, said in an interview. "It kind of started with the abstract sense, and minimalism was a part of that."

"We didn't go into pop [art] and stuff like that," she added.

Rub likened the Sachs gift to two earlier gifts to the museum: The 1950 gift of Walter and Louise Arensberg, which made the Philadelphia Museum of Art a mecca for all things related to Marcel Duchamp, and enriched the collection with works by Jean Metzinger, Charles Sheeler, Walter Pach, Beatrice Wood, and Elmer Ernest Southard.

In 1952, collector and artist Albert E. Gallatin donated his powerful collection of early modernist work to the museum, including iconic pieces by Picasso, Joan Miró, André Masson, Robert Delaunay, Piet Mondrian, and Jean Arp.

The Sachses have been collecting for more than 40 years. Keith Sachs, 68, former head of a firm that supplied packaging to wine and spirits businesses, has been a trustee of the museum since 1988.

He has been chair of PennDesign and is a graduate of the University of Pennsylvania's Wharton School.

Katherine Sachs began working at the Art Museum public relations department about three decades ago and has since served as a volunteer and as an exhibition scholar. She has worked closely with the department of European art before 1900, and was a co-curator of the museum's 2009 exhibition "Cézanne and Beyond."

She is an emeritus trustee of Penn, and is on the board of the university's Institute of Contemporary Art.

As a couple, they have endowed a chair in contemporary art at Penn and a visiting professorship in fine arts and design, and have seeded Penn's Sachs Fine Arts Program Fund.

"When we started to collect, we never thought of doing anything other than making a gift to some institution," Keith Sachs said in an interview. "We never thought about investment value. . . . We care about Philadelphia. It's a wonderful city and we've made a commitment to the arts along the way."

Three Great Building Blocks

Half Past Three (The Poet), 1911, Marc Chagall, from the collection of Louise and Walter Arensberg, a gift to the Art Museum in 1950.

Philadelphia Museum of Art, The Louise and Walter Arensberg Collection, 1950. © Artists Rights Society (ARS), New York / ADAGP, Paris

The City, 1919, Fernand Léger, from the collection of Albert E. Gallatin, which came to the museum in 1952.

Philadelphia Museum of Art, A. E. Gallatin Collection, 1952. © Artists Rights Society (ARS), New York / ADAGP, Paris

Erdtelephon (Earth Telephone) 1968-71, Joseph Beuys, a recent gift, now on display, from the collection of Keith L. and Katherine Sachs, which picks up where the Arensberg and Gallatin troves left off, in the mid-20th century.

Gift of Keith L. and Katherine Sachs, 2013 © Joseph Beuys / Artists Rights Society (ARS), New York EndText