Preheat the oven to 375° F.
Butter an oblong baking pan—11 by 7 inches or 12 by 8 inches.
Mix together the oatmeal, flour, sugar, and soda until well-blended.
Pour the melted margarine over the dry ingredients and mix until moistened throughout.
(Mixing with the hands works best.) Layer half the oat mixture over the bottom of the pan.
Top with a thin layer of apricot preserves.
Pat into place the remaining oat mixture to form a top layer.
Bake on the middle shelf for 20 minutes.
Cool on a wire rack before cutting; don't remove the bars from the pan until they're cool enough to hold together.
Store the bars in a covered tin with wax paper between layers.