设这桶油有x千克，

1

4

x+

1

4

x-4+19=x
     

1

2

x+15=x
  

1

2

x+15-

1

2

=x-

1

2

x
      15÷

1

2

=

1

2

x÷

1

2

          x=30
答：原来这桶油重30千克．