During his time in Paris, he saw works by artists such as Juan Gris, Paul Klee, Joan Miró, Pablo Picasso, and especially Henri Matisse, whose influence can be seen in the landscapes and rural scenes Guerrero painted after returning to Spain.
Guerrero now became acquainted with many prominent members of the American avant-garde, including the artists Willem de Kooning, Franz Kline, Robert Motherwell, Ad Reinhardt, Mark Rothko, and Theodoros Stamos, and with James Johnson Sweeney, art critic and director of the Guggenheim Museum.
His style continued to evolve through the 1970s and 1980s, "as he created orderly and rhythmic vertical compositions, followed by increasingly dynamic works in which brilliant hues took the lead".
[1] According to art critic Grace Glueck, he was "[k]nown for big, vibrantly colored paintings whose abstract imagery suggested landscape, primitive architecture and atmospheric events".
[2] His work is held by several prominent collections, including those of the Guggenheim, Whitney and Brooklyn Museums in New York, and from 2000 in the Centro José Guerrero, Granada.